The goal of this research is to understand transposable element activity and its control in the nematode Caenorhabditis elegans. The process of transposition is a major source of spontaneous mutation in a wide range of organisms, including humans. Understanding how these elements transpose and excise and how these events are regulated is central to our understanding of the mechanisms by which mutations arise and the factors that contribute to their occurrence. In addition, the elements under investigation exhibit very different behavior in somatic cells and germ cells. This provides the opportunity to study a basic genetic process independently in these fundamentally different cell types. Genetic and molecular approaches will be combined to investigate important features of four C elegans transposon families: Tc1, Tc3, Tc4, and Tc5. The proposed studies will identify factors required for transposition and excision of each element, and the sequences these factors interact with to promote element mobility. This information is critical for understanding how these elements move and how that movement is regulated. A major outstanding question is the source of the transposase responsible for the activity of each element family. This question must be resolved before questions of transposase function and regulation can be addressed; it will be the primary focus of the proposed studies. Open reading frames (ORFs) contained within these elements represent likely sources of such transposase factors. To determine if these ORFs are expressed, sensitive methods will be used to detect the predicted RNA and protein products. Germ-line activity of Tc3, Tc4, and Tc5 has been detected only in genetic backgrounds containing the mutator mutation mut-2(r459). Genetic methods will be used to determine. if the activity of these elements is indeed mut-2-specific. This information will be important for understanding the regulation of these elements, and it will provide a functional assay for cloning and analysis of mut-2. Genetic mosaic analysis will be used to address the question of somatic activity of these elements. Tc1 is highly active in the soma, however the level of somatic activity for Tc3, Tc4, and Tc5, if any, is unknown. Sequences within each element required in cis for their mobility will be identified. These represent potential sites of action for the transposases. Finally, nucleotide sequences of sites of insertion and excision of Tc3, Tc4, and Tc5 will be determined. These results will be compared with available data for Tc1, providing important information about the extent to which these different element families might respond to the same transposases.